02 Core Java IntroTo Language

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An Introduction

Java Technology


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Confidential Mr. Anuj

Agenda

Fundamentals

Operators

Flow Controls


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Confidential Mr. Anuj 3

Java Source File Structure

Java Keywords

Identifiers

Literals

Variables and Data Types

Variable Declaration and Initialization

Operators

Primitive Casting

Flow Controls

Outline


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At the end of this section, you should be able to: Recognize and create correctly constructed source code

Recognize and create correctly constructed declarations

Distinguish between legal and illegal identifiers

Describe all the primitive data types and the ranges ofthe integral data types

Recognize correctly formatted data types

Learn to properly declare and initialize variables

Understand the contents of the argument list of anapplications main() method

Objectives


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Objectives (continued)

Operators: Learn to use: Unary operators

Arithmetic operators

String operators

Relational operators

Conditional operators

Logical operators

Assignment operators

Be familiar with object, shift and bitwise operators

Identify the order of evaluation and change its precedence

Learn how to cast primitive data types


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Objectives (continued)

Flow Controls: Learn syntax and correct use of:

if-else() statement

switch() statement

while() statement

do-while() statement

for() statement

break, continue and label statements

Introduce the concept of return statement


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/** Created on Jul 14, 2005** First Java Program*/

package com.jds.sample;import java.util.*;

/*** @author JDS*/

public class JavaMain {

public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");

}}

class Extra {/** class body*/

}

1. Package declaration

Used to organize a collection ofrelated classes.

2. Import statement

Used to reference classes anddeclared in other packages.

3. Class declaration

A Java source file can have several

classes but only one public class is

allowed.

declaration order




1. Single Line Comment

// insert comments here

2. Block Comment

/*

* insert comments here

*/

3. Documentation Comment

/**

* insert documentation

*/



/*** @author JDS*/



}}


}


Comments

Tabs and spaces are ignored bythe compiler. Used to improvereadability of code.

Whitespaces





/*** @author JDS*/



}}


}

Every java program includes at

least one class definition. Theclass is the fundamentalcomponent of all Java programs.

A class definition contains all thevariables and methods that makethe program work. This is

contained in the class bodyindicated by the opening andclosing braces.


Class





/*** @author JDS*/



}}


}


Braces are used for groupingstatements or block of codes.

The left brace ({) indicatesthe beginning of a class body,

which contains any variablesand methods the class needs.

The left brace also indicatesthe beginning of a methodbody.

For every left brace that

opens a class or method youneed a corresponding rightbrace (}) to close the class ormethod.

A right brace always closesits nearest left brace.

Braces





/*** @author JDS*/



}

}


}


This line begins the main()

method. This is the line at whichthe program will begin executing.

main() method

Declares a parameter namedargs, which is an array of String.

It represents command-linearguments.

String args[]





/*** @author JDS*/



}

}


}


A complete unit of work in aJava program.

A statement is alwaysterminated with a semicolon andmay span multiple lines in yoursource code.

Java statement

Semicolon (;) is the terminating

character for any java statement.

Terminating characterThis line outputs the stringWelcome to Java! followed by

a new line on the screen.

System.out.println()



true

strictfp

null

implements

extends

char

transient

static

new

if

else

catch

throws

short

native

double

case

throw

return

long

for

do

byte

while

this

public

interface

float

default

break

volatile

synchronized

protected

int

finally

continue

boolean

void

switch

private

instanceof

final

assert

try

super

package

import

false

class

abstract

Java Keywords

gotoconst


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printMeis not the same as PrintMe

Identifiers

An identifieris the name given by aprogrammer to a variable, statementlabel, method, class, and interface

An identifier must begin with a letter,$ or _

Subsequent characters must beletters, numbers, $ or _

An identifier must not be a Javakeyword

Identifiers are case-sensitive

Incorrect Correct

3strikes strikes3Write&Print Write_Print

switch Switch


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A literalis a representation of a value of a particular type

Literals

Type Examples & Values

boolean true false

character a \uFFFF' \777

integer 123 123L O123 Ox123

floating-point 123.5 123.5D 123.5F 123.5e+6

object test null

escape sequences \n \t \b \f \r \ \ \\


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Variable and Data Types

A variableis a named storage location used to representdata that can be changed while the program is running

A data typedetermines the values that a variable cancontain and the operations that can be performed on it

Categories of data types:

1. Primitive data types

2. Reference data types


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What is strongly typed means?

Java is what is known as a strongly typedlanguage.

That means that Java is a language that will only accept specific values

within specific variables or parameters.

Some languages, such as JavaScript, are weakly typed languages. This

means that you can readily store whatever you want into a variable.


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Here is an example of the difference between strongly typedand weakly typed languages:

JavaScript (weakly typed)

1: var x; // Declare a variable

2: x = 1; // Legal

3: x = "Test"; // Legal

4: x = true; // Legal

Java (strongly typed)

1: int x; // Declare a variable of type int

2: x = 1; // Legal

3: x = "Test" // Compiler Error

4: x = true; // Compiler Error


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Primitive Data Types

Type Bits Lowest Value Highest Value

boolean (n/a) false true

char 16 '\u0000' [0] '\uffff' [216-1]

byte 8 -128 [-27] +127 [27-1]

short 16 -32,768 [-215] +32,767 [215-1]

int 32 -2,147,483,648 [-231] +2,147,483,647 [231-1]

long 64 -9,223,372,036,854,775,808 [-263] +9,223,372,036,854,775,807 [263-1]

float 32 1.40129846432481707e-45 3.40282346638528860e+38

double 64 4.94065645841246544e-324 1.79769313486231570e+308

Primitive data types represent atomicvalues and are built-in to Java

Java has 8 primitive data types


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Reference Data Types

Reference data types represent objects

A referenceserves as a handle to the object, it isa way to get to the object

Java has 2 reference data types

1. Class

2. Interface


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Declaring a variable with primitive data type

int age = 21;

Declaring a variable with reference data type

Date now = new Date();

String name =

Jason

;

Variable Declaration & Initialization

identifier

name

primitive

type

initial

value

identifiername

referencetype

initialvalue


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Primitive Type Declaration

Identifiername

type

int age;

stack

age = 17;

valueIdentifiername

age

MEMORY

declaration

initialization/assignment

allot space to memory

017


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The heap

Car object

Values

Reference Type Declaration

type

Car myCar;

myCar = new Car(Bumble Bee);

Identifiername

Bumble Bee

memory address

location

allot space to memory

reference

myCar

Identifiername


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Class Account

int num;

char type;

double balance;

num = 101;

type = S

balance = $1000.00 ;

Account obj1

num = 241;

type = C

balance = $4890.00 ;

Account obj2

Memory

0x 0fed02e

0x 0fc024b


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Member VariablesDeclared inside the classbut outside of all methods.Accessible by all methodsof the class.

Local Variables Availableonly within the methodwhere they were declared.

Method parameters havelocal scope.

Scope of Variable

public class HelloWorld {//accessible throughout the class

String name;

public void otherMethod(){

float salary = 15000.00f;

//cant access age variable from here}

public static void main(String args[ ]) {

//cant access salary variable from here

int age=17;

//cant access ctr variable from herefor (int ctr=0 ; ctr


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Fundamentals

Operators

Flow Controls

Agenda


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Unary operators

Arithmetic operators

String operator

Relational operators

Conditional operator Logical operator

Assignment operators

Object operators

Shift operators

Bitwise operators

Evaluation order

Primitive Casting

Operators and Assignments


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Unary Operators

Unary operators use only one

operand

++ Increment by 1, can be prefix or postfix

-- Decrement by 1, can be prefix or postfix

+ Positive sign

- Negative sign

int num=10;

System.out.println("incrementing/decrementing...");

System.out.println(++num);

System.out.println(--num);System.out.println(num++);

System.out.println(num--);

System.out.println("setting signs...");

System.out.println(+num);

System.out.println(-num);

incrementing/decrementing...

11

10

10

11setting signs...

10

-10

Sample code: Sample output:


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Arithmetic Operators

Arithmetic operators are used for basic

mathematical operations

+ Add

- Subtract

* Multiply

/ Divide

% Modulo, remainder

int num1=15, num2=10;

System.out.println("calculating...");

System.out.println(num1 + num2);

System.out.println(num1 - num2);System.out.println(num1 * num2);

System.out.println(num1 / num2);

System.out.println(num1 % num2);

calculating...

25

5

150

15

Sample code: Sample output:


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String Operator

String operator (+) is used to concatenate operands If one operand is String, the other operands are converted to String

String fname = "Josephine", lname = Luv", mi = "T";

String fullName = lname +", " + fname +" " + mi + ".";

String nickName = "Jessy";

int age=21;

System.out.println("My full name is: "+ fullName);

System.out.println("You can call me "+ nickName +"!");

System.out.println("I'm "+ age +" years old.");

My full name is: Luv, Josephine T.

You can call me Jessy!

I'm 21 years old.

Sample code:

Sample output:


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Relational Operators

Relational operators are used to compare values boolean values cannot be compared with non-boolean values Only object references are checked for equality, and not their states Objects cannot be compared with null null is not the same as

< Less than

Greater than

>= Greater than or equal to

== Equals

!= Not equals


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Relational Operators

String name1 = "Marlon"; int weight1=140, height1=74;

String name2 = "Katie"; int weight2=124, height2=78;

boolean isLight = weight1 < weight2, isLightEq = weight1 height2, isTallEq = height1 >= height2;

System.out.println("Is " + name1 + " taller than " + name2 + "? " + isTall);

System.out.println("Is " + name1 + " taller or same height as " + name2 + "? " + isTallEq);

boolean isWeighEq = weight1 == weight2, isTallNotEq = height1 != height2;

System.out.println("Is " + name1 + " same weight as " + name2 + "? " + isWeighEq);

System.out.println("Is " + name1 + " not as tall as " + name2 + "? " + isTallNotEq);

System.out.println("So who is heavier?");

System.out.println("And who is taller?");

Is Marlon lighter than Katie? false

Is Marlon lighter or same weight as Katie? false

Is Marlon taller than Katie? false

Is Marlon taller or same height as Katie? false

Is Marlon same weight as Katie? false

Is Marlon not as tall as Katie? true

So who is heavier?

And who is taller?

Sample code:

Sample output:


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The ternary operator (?:) provides a handy way to code simple if-else()

statements in a single expression, it is also known as the conditional operator If condition is true, then exp1 is returned as the result of operation

If condition is false, then exp2 is returned as the result of operation

Can be nested to accommodate chain of conditions

Conditional operator

condition ? exp1 : exp2;

int yyyy=1981, mm=10, dd=22;

String mmm = mm==1?"Jan":mm==2?"Feb":mm==3?"Mar":mm==4?"Apr":mm==5?"May":mm==6?"Jun":

mm==7?"Jul":mm==8?"Aug":mm==9?"Sep":mm==10?"Oct":mm==11?"Nov":mm==12?"Dec":"Unknown";

System.out.println("I was born on " + mmm + " " + dd + ", " + yyyy);

I was born on Oct 22, 1981

Sample code:

Sample output:

Syntax:


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Logical Operators

Logical operators are used to compareboolean expressions

! inverts a boolean value & | evaluate both operands && || evaluate operands conditionally

! NOT

& AND

| OR

^ XOR

&& Short-circuit AND

|| Short-circuit OR

Op1 Op2 !Op1 Op1 & Op2 Op1 | Op2 Op1 ^ Op2 Op1 && Op2 Op1 || Op2

false false true false false false false false

false true true false true true false true

true false false false true true false true

true true false true true false true true

Truth Table


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Similar to the Boolean operators, but with an added ability to

short-circuit part of the process, using a couple of mathematicalrules:

If the left operand of an && operation is false, the result isautomatically false, and the right operand is not evaluated

If the left operand of an || operation is true, the result isautomatically true, and the right operand is not evaluated

Boolean Complement ( ! ):

The NOT function inverts the value of boolean

Short-circuit Logical Operators (&&,|| and !)

boolean a = (5>8) && (8>5);false;

boolean b = (8>5) || (5>8);true;

boolean c = !b;false;


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Logical Operators

int yrsService=8;

double perfRate=86;

double salary=23000;

char position='S';

// P-probationary R-regular, S-supervisor, M-manager, E-executive, T-top executive

boolean forRegular, forSupervisor, forManager, forExecutive, forTopExecutive;

forRegular = yrsService>1 & perfRate>80 & position=='P'& salary5 & perfRate>85 & position=='R'& salary7 & perfRate>85 & position=='S'& salary10 & perfRate>80 & position=='M'& salary10 & perfRate>80 & position=='E'& salary


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Assignment Operators

Assignment operators areused to set the value of avariable

= Assign

+= Add and assign

-= Subtract and assign

*= Multiply and assign

/= Divide and assign

%= Modulo and assign

&= AND and assign

|= OR and assign

^= XOR and assign

double unitPrice=120, qty=2, salesAmount;double discRate=15, discAmount, vatRate=10, vatAmount;

// compute gross sales

salesAmount = unitPrice * qty;

System.out.println("Gross Sales: " + salesAmount);

// compute tax

vatRate /= 100;vatAmount = salesAmount * vatRate;

salesAmount += vatAmount;

System.out.println("Tax: " + vatAmount);

// compute discount

discRate /= 100;

discAmount = salesAmount * discRate;

salesAmount -= discAmount;

System.out.println("Discount: " + discAmount);

System.out.println("Please pay: " + salesAmount);

Gross Sales: 240.0

Tax: 24.0

Discount: 39.6

Please pay: 224.4

Sample code:

Sample output:


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Casting

Castingis converting from one data type to another

Implicit castingis an implied casting operations

Explicit castingis a required casting operations

Primitive castingis converting a primitive data type to another

Widening conversionis casting a narrower data type to a broader

data type Narrowing conversionis casting a broader data type to a narrower

data type

Reference castingis converting a reference data type to another

Upcastingis conversion up the inheritance hierarchy

Downcastingis conversion down the inheritance hierarchy Casting between primitive and reference type is not allowed

In Java, casting is implemented using () operator


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Primitive Casting Flow

byte short int long float double

char

widening conversion

narrowing conversion


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Primitive Casting Rule

arithmetic implicit widening conversion

relational implicit widening conversion

shift implicit widening conversion

bitwise implicit widening conversion

assignment implicit widening conversion (if target is broader )

parameter passing implicit widening conversion (if formal parameter is broader)

logical none

ternary ?: noneboolean none

(all others) explicit casting (narrowing or widening conversion)


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Implementing Primitive Casting

public static voidmain(String args[]) {short age = 20;char sex = M;byte iq = 80;int height = 64;long distance =300;float price = 99.99f;

double money = 500.00;

age = sex; // will this compile?sex = iq; // will this compile?iq = (byte) height; // will this compile?distance = height; // will this compile?

price = money; // will this compile?sex = (char) money; // will this compile?

}


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Evaluation order of operators in Java is as follows:

Unary (++ -- + - ~ ())

Arithmetic (* / % + -)

Shift (> >>>) Comparison (< >= instanceof == !=)

Bitwise (& ^ |)

Short-circuit (&& || !)

Conditional (?:) Assignment (= += -= *= /=)

Summary of Operators


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Fundamentals Operators

Flow Controls

Agenda


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Flow Controls

if-else() statement

switch() statement

while() statement

do-while() statement

for() statement

break statement

continue statement

Statement label


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Types of Flow Control

1. Sequential Perform statements in the order

they are written

1. Selection Perform statements based on

condition

1. Iteration Perform statements repeatedly

based on condition


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if-else() Construct

if-else() performs statements based on two conditions Condition should result to a boolean expression If condition is true, the statements following if are executed If condition is false, the statements following else are executed

Can be nested to allow more conditions

if (condition) { // braces optional

// statement required

}

else { // else clause is optional

// statement required

}

int age=10;

if (age < 10) {

System.out.println("You're just a kid.");

} else if (age < 20){System.out.println("You're a teenager.");

} else {

System.out.println("You're probably old...");

}

Syntax:

Example:

You're a teenager.Output:


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switch() construct

switch() performs statements based on multiple conditions exp can only be char byte short int, val should be a unique constant of exp

case statements falls through the next case unless a break is encountered default is executed if none of the other cases match the exp

switch (exp) {

caseval:

// statements here

caseval:

// statements here

default:

// statements here

}

char sex='M';

switch (sex){

case'M':

System.out.println("I'm a male.");break;case'F':

System.out.println("I'm a female.");break;

default:

System.out.println("I am what I am!");

}

Syntax:

Example:

I'm a male.Output:


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while() loop

while() performs statements repeatedly whilecondition

remains truewhile (condition) { // braces optional

// statements here

}

int ctr=10;

while (ctr > 0) {System.out.println("Timer: " + ctr--);

}

Syntax:

Example:

Timer: 10

Timer: 9

Timer: 8

Timer: 7Timer: 6

Timer: 5

Timer: 4

Timer: 3

Timer: 2

Timer: 1

Output:


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do-while() loop

do-while() performs statements repeatedly (at least once) while

conditionremains truedo

// statements here

while (condition);

int ctr=0;

do

System.out.println("Timer: " + ctr++);

while (ctr < 10);

// next statement

Syntax:

Example:

Timer: 0

Timer: 1

Timer: 2

Timer: 3Timer: 4

Timer: 5

Timer: 6

Timer: 7

Timer: 8

Timer: 9

Output:


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for() loop

for() performs statements repeatedly based on a condition

Init is a list of either declarations or expressions, evaluated firstand only once Conditionis evaluated beforeeach iteration

Expis a list of expressions, evaluated aftereach iteration

All entries inside () are optional, for(;;) is an infinite loop

for (init; condition; exp) { // braces optional

// statements here

}

for (int age=18; age


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break

break exits loops and switch() statements

break;

boolean isEating=true;

int moreFood=5;

while (isEating) {

if (moreFood


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continue

continue is used inside loops to start a new iteration

continue;

for (int time=7; time


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Statement Label A label is an identifier placed before a statement, it ends with : break labelNameis used to exit any labelled statement

continue labelName is used inside loops to start a new iteration of the labeled loop

labelName:

break labelName;

continue labelName;

int[] scores = {3,9,10,0,8,10,7,1,9,8};

outer:

for (int i=0; i


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Example 1:

public int sum(int x, int y) {return x + y;

}

Example 2:

public int sum(int x, int y) {

x = x + y;

if (x < 100){return x;

}else{

return x + 5;

}

}

Example 2:public void getSum(int x) {

System.out.println(x);

return;

}

return branchingstatement is used toexit from the currentmethod.

Two forms:

return ; return;

return


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Key Points

A Java source file can include package, import and class

declarations in that order The main() method is the start of execution of a Java

application

Each Java statement is terminated by a semicolon ;

Identifiers are case-sensitive Java keywords cannot be used as identifiers

Each variable must be declared with a data type

There are 8 primitive data types: boolean, char, byte,

short, int, long, float and double There are 3 reference data types: class, array and

interface


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Key Points (continued)

Use unary, arithmetic operators for basic mathematical

operations

Use string operator to concatenate strings

Use relational operators to compare objects

Use conditional operator as alternative to if-else()

statement

Use logical operators to compare boolean values

Use assignment operators to assign values to variables

Get familiar with object, shift and bitwise operators Java evaluates operators in order of precedence

Castingis converting one data type to another

Ke Points


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Key Points

if() and switch() are used for branching statements

while(), do-while() and for() are used for iterating

statements

break, continue and labelare used to branch inside

loops


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http://www.java.sun.com

http://www.java.com

http://www.java.net

http://javaboutique.internet.com

http://javaboutique.webdeveloper.com

http://www.javaworld.com http://www.developer.com

http://javalobby.org

http://freewarejava.com

http://onjava.com

http://javaranch.com http://www.cafeaulait.org

http://www.java.about.com

http://www.javacoffeebreak.com

Java Online Resources
http://www.java.sun.com/http://www.java.com/http://www.java.net/http://javaboutique.internet.com/http://javaboutique.webdeveloper.com/http://www.javaworld.com/http://www.developer.com/http://javalobby.org/http://freewarejava.com/http://onjava.com/http://onjava.com/http://onjava.com/http://freewarejava.com/http://freewarejava.com/http://javalobby.org/http://javalobby.org/http://www.developer.com/http://www.developer.com/http://www.javaworld.com/http://www.javaworld.com/http://javaboutique.webdeveloper.com/http://javaboutique.webdeveloper.com/http://javaboutique.internet.com/http://javaboutique.internet.com/http://www.java.net/http://www.java.com/http://www.java.com/http://www.java.sun.com/http://www.java.sun.com/


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Tutorials:

http://java.sun.com/docs/books/tutorial http://www.ibiblio.org/javafaq/javatutorial.html

http://www.javacoffeebreak.com/tutorials/index.html http://www.cafeaulait.org/course/ http://oopweb.com/Java/Documents/IntroToProgrammingUsingJav

a/VolumeFrames.html

FAQs: http://java.sun.com/products/jdk/faq.html

http://www.ibiblio.org/javafaq/javafaq.html http://www.apl.jhu.edu/~hall/java/Beginners-Corner.html http://www.norvig.com/java-iaq.html http://www.jguru.com/faq/subtopics.jsp?topic=JavaLanguage http://www.javacoffeebreak.com/faq/

Java Online Resources

Q i d C


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Questions and Comments